http://confocal-microscopy-list.275.s1.nabble.com/Readout-noise-in-sCMOS-cameras-tp7588012p7588020.html
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> Dear Jeremy,
>
> Of course you correct.
>
> I stated it as I did because I find that people who correctly understand
> that the signal-to-Poisson Noise ratio increases with the sqrt of the
> signal level forget that the absolute value of the uncertainty in the
> signal level increases with the sqrt of the signal level, i.e., they are
> surprised to see that the “grass” on the signal of apparently uniform
> bright areas is much greater than that on dark areas.
>
> While it may be convenient to estimate that the noise in low contrast
> widefield image from a CCD can be approximated as being Gaussian, this
> really is not true when applied to images from, for instance, an slow-scan
> CCD image from a confocal. In the latter, many pixels will be essentially
> black and in these pixels, the noise will be Gaussian and represent the
> read noise of the charge-to-voltage converter (much of which is Johnson
> noise related to the electron statistics of small, fairly constant
> currents). However, it would be a mistake to think that this same Gaussian
> accurately defines the uncertainty of signals from the brighter parts of
> the image (>100 photoelectrons?).
>
> sCMOS has a whole raft of other noise terms and as noted the noise in
> their output is poorly estimated by a Gaussian, particularly on images
> having high-contrast.
>
> Great sensors though!
>
> JP
>
> James and Christine Pawley, 5446 Burley Place, Box 2348, Sechelt BC,
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>
> On Mar 6, 2018, at 2:47 AM, Jeremy Adler <
[hidden email]
> <mailto:
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>
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> Dear James,
> a minor point from your interesting post.
>
> "Poisson Noise get bigger as the signal increases!"
>
> This is true as an absolute measure of the size of the variation around
> the mean but your statement could be misinterpreted as a preference for
> detecting fewer PEs.
> Perhaps adding - but is smaller as a fraction of the signal
> An average of 16 PEs has a standard deviation of 25% while for 256 PEs
> the SD drops to around 6% and to 3% for 1024.
>
>
> Jeremy Adler
> IGP, Uppsala U, Sweden
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> -----Original Message-----
> From: Confocal Microscopy List [mailto:
[hidden email]]
> On Behalf Of JAMES B PAWLEY
> Sent: den 6 mars 2018 07:22
> To:
[hidden email]
> Subject: Re: Readout noise in sCMOS cameras
>
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> Dear Sripad,
>
> In a CMOS chip, every pixel has its own read amp. All of these vary
> slightly in gain and DC-offset. So the raw output from a a black (no light)
> image would have a noise term related to how much the offsets of the pixel
> amps varied and a uniform white image would have Poisson noise on the photo
> charge plus a noise term mostly related to the variation in the gains of
> the pixel amplifiers.
> In an sCMOS chip to these uncertainties must be added variations in the
> gain and offer of the 4,000-plus separate ADCs mounted at the edges of the
> chip. An effort is made to correct for the multi-amplifier and
> multi-digitizer noise by “flat fielding” the raw data from the chip using
> data from previous “black” and “white” images, The system works quite well
> but as the white image always involves a lot of charge, its Poisson noise
> (sqrt of n) is large and this can skew the results. So can using the chip
> at a different temperature, dwell time or pixel clock than was used for the
> “black” and “white” images. Other sources on non-“Gaussian” noise include
> “hot pixels” (perhaps leaky photodiodes that are sometimes flagged and
> removed by the camera system software).
>
> Indeed, the noise spectrum in these low-light systems is almost never
> “Gaussian”. Even if the electronic noise (that signal variation which
> becomes evident when reading the same pixel with no light signal) seems
> Gaussian, it is usually caused by Poisson Noise (Or Johnson noise)
> affecting the small number of electrons that constitute the (fairly table
> currents passing through the elements of the charge amplifier. And of
> course, at signal levels of more than a few dozen photoelectrons, Poisson
> Noise on the PE number soon dominates most other noise sources (not hot
> pixels).
>
> Gaussian noise is just easier to think about, and easier to model. We
> should remember that in low-light photodetectors, it is almost never
> appropriate. (Poisson Noise get bigger as the signal increases!).
>
> Best,,
>
> JP
> James and Christine Pawley, 5446 Burley Place, Box 2348, Sechelt BC,
> Canada, V0N3A0
[hidden email]<mailto:
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>
> On Mar 5, 2018, at 9:54 AM, S Ram <
[hidden email]<mailto:s
>
[hidden email]>> wrote:
>
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> Hello Gerhard,
> This is a slightly off-topic question in connection to your recent
> response to the thread on the choice of sCMOS cameras.
>
> You made a comment that the distribution of noise in sCMOS is not Gaussian.
>
> Can you clarify whether you meant noise during the readout process (charge
> to voltage conversion step)? If it is not Gaussian, what is the underlying
> noise process? Is there any literature that you can point me to?
>
> Thanks.
>
> Sripad
>
>
>